The present invention relates generally to a mass air flow sensor and more particularly with reduced costs and improved efficiency and performance.
Mass air flow sensors (MAFS) are commonly used in internal combustion engines to maintain an optimal air/fuel ratio. Mass air flow sensors often work on the xe2x80x9chot wirexe2x80x9d principle where a constant temperature is maintained in a xe2x80x9chotxe2x80x9d element which is often a positive coefficient resistor. The hot element is heated by the electrical current passing through it and is positioned in the approaching air flow or in an air flow sampling tube or xe2x80x9cbypassxe2x80x9d. A second ambient or xe2x80x9ccoldxe2x80x9d element is also positioned in the same fashion and is electrically in parallel with the hot element. As the air flows over the hot element, it cools the element down, effectively reducing the resistance of the elements. The lower resistance allows more current to flow in order to maintain a constant temperature difference between the hot and cold elements. This change in current results in a change in voltage which is sent to the engine computer.
Although mass air flow sensors are known in the automotive industry, existing MAFS designs can have undesirable characteristics. One known design utilizes a differential pressure bypass to produce the needed velocity increase past the hot sensor for measuring low air flows at engine idle. This design, however, can produce a significant pressure drop between the inlet and the outlet of the MAFS. This pressure drop contributes to the total dissipative losses of the air induction system, in which the MAFS is utilized, thereby reducing the efficiency of the AIS (Air Induction System) in supplying air to the engine. This can be highly undesirable.
In an attempt to reduce the magnitude of the pressure drop across the MAFS, some existing differential pressure bypass designs attempt to limit the sensor""s intrusion into the approaching air flow. This, however, can generate the need for tight tolerances from mounting the MAFS within the air flow. Variation in mounting these MAFS designs can result in variability of the output and thereby negatively affect engine performance. The tight tolerances required to minimize such variations can result in undesirable cost increases to the mass air flow sensor and the air induction system.
Current MAFS designs also have the undesirable characteristic of disposing the sensor elements to the approaching air flow. This exposure of the sensing elements can increase the risk of contaminating the sensing elements due to particles in the air flow. Contamination of the sensing elements can potentially cause a shift in the output with the mass air flow sensor. It is known that shifts in the mass air flow sensor output can cause the air/fuel mixture to be too lean and result in detonation and damage to the engine.
It would, therefore, be highly desirable to have a mass air flow sensor design that reduce the pressure drop of air passing through a MAFS eliminates the need for tight tolerances and reduces the risk of contaminating the sensing elements.
It is therefore an object of the present invention to provide a mass air flow sensor with increased efficiency, reduced cost, and reduced sensitivity to contamination.
In accordance with the objects of this invention, a mass air flow sensor is provided. The mass air flow sensor includes a housing. Within the housing is positioned an air foil element. At least one sensing element is surface mounted on the air foil element.